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Title: Phytotoxic Properties of Monoterpenes on Silybum Marianum (L.) Gaertn. and their Inhibitory Effect on Carbonic Anhydrase Activity
Authors: Samir A.M. Abdelgaleil; Neama A. Gouda ; Mona M.G. Saad
Aff: Department of Pesticide Chemistry and Technology, Faculty of Agriculture, El-Shatby, Alexandria University, Alexandria 21545, Egypt
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Keywords: Monoterpenes; Herbicidal Activity, Silybummarianum; Carbonic Anhydrase, Mode of Action
Abstract:Background:Monoterpenes are common essential oil constituents that provide the essence and the odor of a plant.The natural pesticidal properties of monoterpenes make them useful as potential alternative pest control agents as well as good lead compounds for the development ofsafe, effective, and fully biodegradable pesticides. Monoterpeneshave been reported to possessallelopathic and herbicidal properties.Objective:This study has been under taken to investigate the effect of tenmonoterpenes, namely camphene, (R)-camphor, (R)-carvone, 1,8-cineole, (S)- fenchone, geraniol, (S)-limonene, (R)-linalool, (1R,2S,5R)-menthol and thymol, on seed germination and seedling growth of Silybummarianumand toevaluate theirinhibitory effects on carbonic anhydrase activity. Results:All monoterpenes reduced seed germination and inhibited seedling growth but to varying extents. Among the tested compounds, thymol was the most potent seed germination inhibitor at the tested concentrations of 0.5, 1 and 2mM.Four compounds, thymol, (1R,2S,5R)-menthol, (R)- camphor and (R)-carvone, caused complete inhibition of seed germinationat concentration of 4 mM.Furthermore, the monoterpenes strongly inhibited root growth of the weed with thymol and camphene being the most potent compounds as EC50 value for both compounds was 0.40 mM, while(R)-linalool, geraniol and 1,8-cineole showed the weakest root growth inhibition activity. On the other hand, the results of shoot growth inhibition revealed that thymolcaused the highest growth inhibition, followed by (1R,2S,5R)-menthol and (R)-camphor with EC50 values were 0.40, 0.43 and 0.50 mM, respectively. Six of tested monoterpenes were tested for theireffect on carbonic anhydrase (CA) activity. The monoterpenes strongly inhibited the enzyme with (S)- fenchone (I50 = 0.08 mM) being the most potent, followed by (R)-camphor (I50 = 0.11mM) and 1,8-cineole (I50 = 0.12 mM). This is the first report on the inhibitory effects of monoterpenes oncarbonic anhydrase.The structure-activity relationship of the tested compounds was disclosed. Conclusion:The results of this study suggest that the monoterpenes,thymol, (1R,2S,5R)-menthol, (R)-camphor, camphene and (R)-carvone possess strong phytotoxic potential and can thus serve as lead compounds for the development of new bioherbicides.